Generally, a stapler includes a base which has a binding table at a front end portion thereof, and sheets of paper are placed on the binding table. The stapler further includes a handle, a driver provided at a distal end of the handle, and a magazine which is positioned above the sheets of paper. When the handle is pressed down, a staple inside the magazine is downwardly driven out by the driver. Legs of the staple which has penetrated through the sheets of paper are folded along a back face of the sheets of paper by a clincher groove in a clincher part which is provided below the sheets of paper. As the result, the sheets of paper are bound.
The number of the sheets of paper to be bound is not always the same, and may be two or three, and sometimes may be forty or fifty. A thickness of the sheets of paper through which the staple has to penetrate is different depending on the number of the sheets. In a case in which the number of the sheets is small, the sheets of paper have a small thickness, and hence, the staple is not stably held by the sheets of paper in a state in which the staple has penetrated through the sheets of paper. Further, the sheets of paper may sometimes move while the handle is being pressed with force, and in such a case, the legs of the staple may sway.
Moreover, depending on the thickness of the sheets of paper to be bound, a striking angle of the legs of the staple at the time when they penetrate the sheets of paper subtly varies, and positions at which the legs of the staple come into contact with the clincher groove after penetrating the sheets of paper also subtly vary.
For such reasons, there is known a stapler which can bind a number of sheets of paper such as forty or fifty, in which sufficient length and width of a clincher groove are ensured and in which respective end portions of the clincher groove in a widthwise direction are curved such that an inner face of the clincher groove has an arcuate sectional shape (see, e.g., JP 11-28682 A).
Further, there is also known a stapler which is configured such that a clincher groove is movable in up and down directions instead of being fixed to the base. In this type of stapler, when a staple is driven out by downwardly moving a driver, a clincher groove is also moved downward until the legs of the staple penetrate the sheets of paper. Thereafter, by further moving the driver downward, the legs of the staple are inwardly folded by the clincher groove. Also in this stapler, a width of the clincher groove in a longitudinal direction of the stapler is set to be larger than a width of a side face of the staple, as shown in FIG. 6A. A bottom face of the clincher groove has a flat face section which is substantially perpendicular to a striking direction of the staple.
However, although a driver 40 is provided at a distal end of the handle perpendicularly with respect to the handle, the handle is rotatable. Therefore, when striking the staple, a lower end face 41 of the driver 40 is not parallel to the bottom face 43 of the clincher groove 42, but is slightly inclined rearward. In addition, when a user performs a clinching action to fold the legs 10 of the staple on the clincher groove 42 after the legs of the staple have penetrated through the sheets of paper, the entire stapler is likely to be pulled toward the user (i.e., toward a rear side of the stapler). When the stapler moves toward the user, the sheets of paper relatively moves to a front side of the stapler.
Therefore, in a case in which the sheets of paper to be bound has a small thickness, lower ends of the legs 10 of the staple are likely to slide to the front side of the stapler as shown in FIG. 6B, and the legs 10 of the staple are likely to become rearwardly inclined. In a case in which the sheets of paper to be bound has a large thickness, an angle of the sheets of paper becomes unmatched with the bottom face 43 of the clincher groove, and hence, the bent legs 10 becomes likely to move to the front side of the clincher groove. Therefore, also in this case, the legs 10 of the staple are likely to be inclined rearward.
In order to address the disadvantages described above, as shown in FIG. 6C, an attempt was made to incline the entire bottom face 43 of the clincher groove such that a front part of the bottom face 43 becomes higher than a rear part thereof. In this case, the legs 10 of the staple are unlikely to slide forward, but are likely to slide rearward along inclination of the bottom face 43 when the sheets of paper to be bound have a small thickness, resulting in a bad shape of the staple after binding the sheets of paper. In order to prevent the legs 10 of the staple from rearwardly sliding along the inclination of the bottom face 43, it may be considered to stop the slide of the legs 10 of the staple with an upright wall 44 of the clincher groove. However, in this case, there is a problem that positional accuracy of the upright wall 44 is strictly required.